Structures can be installed at sea from a floating vessel using either a J-lay configuration where the structure is held vertically on the vessel and dropped vertically into the water and then when it reaches the bottom of the body of water, it lays horizontal, or structures can be installed in a S-lay configuration where the structure is held horizontally on the vessel, drops to the vertical through the body of water, and then rests on the bottom of the body of water in a horizontal configuration. Other configurations for installing a structure from a vessel in a body of water are also known. One limitation on installing such structures in a body of water is the buoyancy of the vessel and the capacity of the tensioner on the vessel to hold the structure, so that the structure is not released into the body of water and does not sink to the bottom.
As oil pipelines have been installed on the bottom of a body of water, as the weight of the pipelines increases and with an increasing depth of the body of water, the capacity of the buoyancy of vessels and the tensioners of vessels is being reached.
Referring now to FIG. 1, a view of a prior art system 100 for installing a structure 114 in body of water 112 is illustrated. System 100 includes vessel 110 with tensioner 120 which is holding structure 114. Structure 114 is being installed on the bottom 116 of body of water 112. Vessel 110 and tensioner 120 keep structure in a vertical configuration when entering the water, and if tensioner 120 were to fail or if vessel 110 to sink, structure 114 would sink to the bottom 116. Vessel 110 and tensioner 120 must have a sufficient capacity to support structure 114 so that it can be installed on bottom 116 in a desired manner.
Referring now to FIG. 2, prior art system 200 for installing structure 214 on bottom 216 of body of water 212 is illustrated. System 200 includes vessel 210 with tensioner 220 and stinger 218. Tensioner 220 holds structure 214 in a horizontal configuration as it enters water, and then structure 214 drops to a vertical configuration, and then back to a horizontal configuration as it lays on bottom 216. Tensioner 220 and vessel 210 must have a sufficient capacity to support structure 214 as it is being installed.
It can be seen from FIGS. 1 and 2 that as the weight of structures 114 and 214 increases, and as the depth of water 112 and 212 increase, there is a need for an increased capacity of vessels 110 and 210 and tensioners 120 and 220.
In deep water applications, for example greater than about 1000 or 2000 meters of depth, there are few vessels that have sufficient capacity to install oil flowlines and other structures. In addition, as the depths of the water increases, the capacity of the vessels must also increase, which leads to increased installation cost, because in general, a vessel with a larger capacity also costs more.
In one example, referring again to FIG. 1, to install a 8.625 inch by 12.75 inch pipe-in-pipe oil flowline structure 114 in 3050 meters of water, a top tension (if structure 114 is dry) is 6780 kN, and if structure 114 becomes flooded, 8510 kN of tension are needed by tensioner 120 to keep structure 114 near vertical (for example a 7° top angle). There are only a small number of vessels that are able to provide such tension, for example, the Heerema Balder in J-lay can provide 10,275 kN of tension. However, at the end of structure 114, a cable is often attached for the abandon and recover procedure to lower structure 114 to the bottom 116. The Heerema Balder's abandon and recover capacity is only 6,850 kN. Therefore, if structure 114 is flooded, and 8510 kN are needed, the Heerema Balder would be unable to complete the installation. In this example, the 8.625 inch by 12.75 inch pipe-in-pipe oil flowline has a weight of 70 kilograms per meter dry and 90 kilograms per meter flooded.
CRP Group Inc. of Houston, Tex., sells pipeline installation buoys, which buoyancy modules can be strapped to a pipeline on board the vessel prior to lowering the pipeline into the water. These buoyancy modules are often released and recovered, for example, with a diver, an ROV, or an acoustic release mechanism. For shallow water applications, the buoyancy modules are filled with a high density polyurethane foam. For mid-water and deepwater pipeline buoyancy modules, a syntactic foam may be used.
Generally, a polyolefin foam, for example, polyethylene may be used in depths up to about 100 meters for buoyancy or insulation applications. A polyurethane foam may also be used in depths up to about 100 meters. Polyurethane foam generally has a density of about 50 to 250 kilograms per meter cubed, with a higher density foam required for deeper water applications.
Co-polymer foams can be used at depths up to 600 or even up to 1000 meters, and have densities of 40 to 400 kilograms per meter cubed.
Syntactic foams are used for installation and buoyancy applications in deeper waters. Syntactic foams are manufactured by placing microspheres of hollow glass or other materials in a polymer matrix. Syntactic foams can be used at depths up to 3000 meters, up to 4000 meters, or more, and have densities of 275 to 650 kilograms per meter cubed.
Generally, with all kind of foams, a higher density foam is required for deeper water applications.
There is a need in the art for systems and/or methods to efficiently install structures in a body of water.